(1) Field of the Invention
The present invention relates to a work-clamp pallet for a machine tool which is attached to a work table to facilitate quick exchange of workpieces on the pallet for improvement of the working efficiency of the machine tool.
(2) Description of the Prior Art
The improvement of productivity of numerically controlled (NC) machine tools such as machining centers the working efficiency as well as precision has been noted in recent years
However, the work-changing remains time-consuming with little improvement made to date. As a result, the proportion of the time required for changing workpieces to the overall working hours has been steadily and rapidly increasing in sharp contrast to that of actual machining time. It is accepted to be a major area for the desired improvement of working efficiency in machine tool operation.
The initial costs of machine tools have also been increasing, keeping pace with their increasing speed and production capacity.
The importance of shortening the time required for changing workpieces on the machine's work table has been recognized for the improvement of the overall working efficiency of the machine so that their high production capacity can be fully utilized.
Of the prior art, considered useful to meet this desire is, among others, the work-clamp pallet described in U.S. Pat. No. 3,899,162. (See FIG. 43.)
Its construction is as described below.
On its base block 201 are arranged 5 pairs of hydraulic cylinders 202, each pair thereof opposing each other. Between the opposing pairs of hydraulic cylinders 202 at a lower level there is provided a centering device 203. In this device 203, an upwardly tapered block 204 is guided by a pair of vertical guides 205 so as to be movable only vertically and is urged upwardly by spring 206.
The piston rod 207 of each hydraulic cylinder 202 has secured to it a positioning block 208 and above it there is fixedly disposed a clamping block 209. The front end face of the positioning block 208 forms an inclined face 210 which comes into contact with the tapered block 204.
In the topside of the clamping block 209 there is provided a recess 212 for engagin workpiece 211 therein. The rear wall face of this recess 212 serves as a clamping face 213 and both side walls thereof serve as right and left positioning faces 214, respectively.
Described below is how it is used and its functions.
First, the base block 201 is placed on the work table of the vertical machine tool and is precisely positioned longitudinally as well as laterally before it is clamped.
Then the workpiece 211 is set in the recesses 212 of each opposing pair of hydraulic cylinders 202. The width of the recess 212 is dimensioned to match that of the workpiece 211, hence the workpiece 211, as it is set in the recesses 212, comes into contact with both right and left positioning faces 214 to be laterally positioned thereby.
Then, when both hydraulic cylinders 202 are simultaneously driven, the workpiece 211 is clamped between the clamping faces 213 of both clamping blocks 209.
The inclined faces 210 of both positioning blocks 208 then come into contact with the tapered block 204 on both sides thereof and are stopped after the tapered block 204 has been forced down against the force of the spring 206.
Thus, the longitudinal position of the workpiece 211 is determind by the tapered block 204, inclined faces 210, both positioning blocks 208, both clamping blocks 209 and both clamping faces 213.
This construction, however, has the following defects or shortcomings:
(1) There is no standard for longitudinal as well as lateral positioning on the machine's work table of the base block of the pallet-clamp pallet, this resulting in a poor positioning precision.
Also, the required positioning procedure is time-consuming and inefficient;
(2) The work-clamp pallet is clamped on the work table of the machine tool as the workpieces thereon are changed.
Hence, the time required for changing workpieces increases with increasing number of workpieces involved which means increased down-time of the machine tool for work-changing and decreased working efficiency thereof;
(3) For precise lateral positioning of workpieces 211, it is necessary to precisely dimension the width of the recess 212 of the clamping block 209 to match that of the workpiece 211 so as to ensure perfect fitting of both.
This means that a different clamping block 209 must be used each time the width of the work 211 is changed.
This means an increased down-time required for changing clamping blocks 209, which is added to the already long work-changing time, further lowering the working efficiency.
Moreover, it is quite expensive and troublesome, for a large number of different size clamping blocks 209 have to be made and kept according to the variety in width of the workpieces involved;
(4) At least two units of hydraulic cylinders 202 are required to clamp one workpiece 211, making the construction of the pallet complicated and being also expensive.
It also means an increased space required for the hydraulic cylinders 202 with the corresponding decrease of the space available for workpieces, hence the number of workpieces that can be placed on the work table of the machine tool is decreased. The required frequency of work-changing is increased and the efficiency of work-changing is affected, these resulting in deterioration of the overall working efficiency of the machine tool; and
(5) For positioning the workpiece 211 only longitudinally, the positioning device 203 and the positioning block 208 are required, hence the construction of the work-clamping pallet is unduly complicated, this resulting in a further increase of its manufacturing cost.
Since both positioning device 203 and positioning block 208 are moving parts, there is an increased risk of error in longitudinal positioning of the work 211, this resulting in a lowered precision of longitudinal machining.
This defect is bound to be aggravated with progressive wear of the moving parts, hence there is much to be desired about its durability.